Low thermal distortion extreme-UV lithography reticle

ABSTRACT

Thermal distortion of reticles or masks can be significantly reduced by emissivity engineering, i.e., the selective placement or omission of coatings on the reticle. Reflective reticles so fabricated exhibit enhanced heat transfer thereby reducing the level of thermal distortion and ultimately improving the quality of the transcription of the reticle pattern onto the wafer. Reflective reticles include a substrate having an active region that defines the mask pattern and non-active region(s) that are characterized by a surface that has a higher emissivity than that of the active region. The non-active regions are not coated with the radiation reflective material.

This invention was made with government support under contract No.DE-AC04-94AL85000 awarded by the U.S. Department of Energy to SandiaCorporation. The government has certain rights to the invention.

FIELD OF THE INVENTION

The invention relates to projection lithography employing soft x-raysand in particularly to reticles that exhibit minimum thermal distortionduring scanning. The invention is particularly suited for systems thatuse a camera that images with acuity along a narrow are or ringfield.The camera employs the ringfield to scan the reflective reticle andtranslate a pattern onto the surface of a wafer.

BACKGROUND OF THE INVENTION

In general, lithography refers to processes for pattern transfer betweenvarious media. A lithographic coating is generally aradiation-sensitized coating suitable for receiving a projected image ofthe subject pattern. Once the image is projected, it is indelibly formedin the coating. The projected image may be either a negative or apositive of the subject pattern. Typically, a “transparency” of thesubject pattern is made having areas which are selectively transparent,opaque, reflective, or non-reflective to the “projecting” radiation.Exposure of the coating through the transparency causes the image areato become selectively crosslinked and consequently either more or lesssoluble (depending on the coating) in a particular solvent developer.The more soluble (i.e., uncrosslinked) areas are removed in thedeveloping process to leave the pattern image in the coating as lesssoluble crosslinked polymer.

Projection lithography is a powerful and essential tool formicroelectronics processing. As feature sizes are driven smaller andsmaller, optical systems are approaching their limits caused by thewavelengths of the optical radiation. “Long” or “soft” x-rays (a.k.a.Extreme UV) (wavelength range of λ=100 to 200 Å (“Angstrom”) are now atthe forefront of research in efforts to achieve the smaller desiredfeature sizes. Soft x-ray radiation, however, has its own problems. Thecomplicated and precise optical lens systems used in conventionalprojection lithography do not work well for a variety of reasons. Chiefamong them is the fact that there are no transparent, non-absorbing lensmaterials for soft x-rays and most x-ray reflectors have efficiencies ofonly about 70%, which in itself dictates very simple beam guiding opticswith very few surfaces.

One approach has been to develop cameras that use only a few surfacesand can image with acuity (i.e., sharpness of sense perception) onlyalong a narrow arc or ringfield. Such cameras then scan a reflectivemask across the ringfield and translate the image onto a scanned waferfor processing. Although cameras have been designed for ringfieldscanning (e.g., Jewell et al., U.S. Pat. No. 5,315,629 and Offner, U.S.Pat. No. 3,748,015), available condensers that can efficiently couplethe light from a synchrotron source to the ringfield required by thistype of camera have not been fully explored. Furthermore, full fieldimaging, as opposed to ringfield imaging, requires severely asphericmirrors in the camera. Such mirrors cannot be manufactured to thenecessary tolerances with present technology for use at the requiredwavelengths.

The present state-of-the-art for Very Large Scale Integration (“VLSI”)involves chips with circuitry built to design rules of 0.25 μm. Effortdirected to further miniaturization takes the initial form of more fullyutilizing the resolution capability of presently-used ultraviolet (“UV”)delineating radiation. “Deep UV” (wavelength range of λ=0.3 μm to 0.1μm), with techniques such as phase masking, off-axis illumination, andstep-and-repeat may permit design rules (minimum feature or spacedimension) of 0.18 μm or slightly smaller.

To achieve still smaller design rules, a different form of delineatingradiation is required to avoid wavelength-related resolution limits. Oneresearch path is to utilize electron or other charged-particleradiation. Use of electromagnetic radiation for this purpose willrequire x-ray wavelengths.

A variety of x-ray patterning approaches are under study. Probably themost developed form of x-ray lithography is proximity printing. Inproximity printing, object:image size ratio is necessarily limited to a1:1 ratio and is produced much in the manner of photographic contactprinting. A fine-membrane mask is maintained at one or a few micronsspacing from the wafer (i.e., out of contact with the wafer, thus, theterm “proximity”), which lessens the likelihood of mask damage but doesnot eliminate it. Making perfect masks on a fragile membrane continuesto be a major problem. Necessary absence of optics in-between the maskand the wafer necessitates a high level of parallelism (or collimation)in the incident radiation. X-ray radiation of wavelength λ≦16 Å isrequired for 0.25 μm or smaller patterning to limit diffraction atfeature edges on the mask.

Use has been made of the synchrotron source in proximity printing.Consistent with traditional, highly demanding, scientific usage,proximity printing has been based on the usual small collection arc.Relatively small power resulting from the 10 mrad to 20 mrad arc ofcollection, together with the high-aspect ratio of the synchrotronemission light, has led to use of a scanning high-aspect ratioillumination field (rather than the use of a full-field imaging field).

Projection lithography has natural advantages over proximity printing.One advantage is that the likelihood of mask damage is reduced, whichreduces the cost of the now larger-feature mask. Imaging or cameraoptics in-between the mask and the wafer compensate for edge scatteringand, so, permit use of longer wavelength radiation. Use of extremeultra-violet radiation (a.k.a., soft x-rays) increases the permittedangle of incidence for glancing-angle optics. The resulting system isknown as extreme UV (“EUVL”) lithography (a.k.a., soft x-ray projectionlithography (“SXPL”)).

A favored form of EUVL is ringfield scanning. All ringfield opticalforms are based on radial dependence of aberration and use the techniqueof balancing low order aberrations, i.e., third order aberrations, withhigher order aberrations to create long, narrow illumination fields orannular regions of correction away from the optical axis of the system(regions of constant radius, rotationally symmetric with respect to theaxis). Consequently, the shape of the corrected region is an arcuate orcurved strip rather than a straight strip. The arcuate strip is asegment of the circular ring with its center of revolution at the opticaxis of the camera. See FIG. 4 of U.S. Pat. No. 5,315,629 for anexemplary schematic representation of an arcuate slit defined by width,W, and length, L, and depicted as a portion of a ringfield defined byradial dimension, R, spanning the distance from an optic axis and thecenter of the arcuate slit. The strip width is a function of thesmallest feature to be printed with increasing residual astigmatism,distortion, and Petzval curvature at distances greater or smaller thanthe design radius being of greater consequence for greater resolution.Use of such an arcuate field allows minimization of radially-dependentimage aberrations in the image. Use of object:image size reduction of,for example, 5:1 reduction, results in significant cost reduction ofthe, now, enlarged-feature mask.

Masks or reticles for EUV projection lithography typically comprise asilicon substrate coated with an x-ray reflective material and anoptical pattern fabricated from an x-ray absorbing material that isformed on the reflective material. In operation, EUV radiation from thecondenser is projected toward the surface of the reticle and radiationis reflected from those areas of the reticle reflective surface whichare exposed, i.e., not covered by the x-ray absorbing material. Thereflected radiation effectively transcribes the pattern from the reticleto the wafer positioned downstream from the reticle. Among the problemsencountered in EUV projection lithography are point-to-pointreflectivity variations. The art is in search of techniques to reducereticle distortions.

SUMMARY OF THE INVENTION

The present invention is based in part on the recognition that thermaldistortion in reticles can be significantly reduced by fabricatingreticles exhibiting improved radiative cooling in vacuum systems. Forexample, this can be achieved by designing the nonactive regions ofreflective reticles not to be coated with the high reflective materialthat is found on the surface of the active region where the pattern isformed. Alternatively, the nonactive regions can be coated with a highemissivity material. By employing emissivity engineering which involvesthe selective placement or omission of coatings on the reticle, theinventive reflective reticle fabricated will exhibit enhanced heattransfer thereby reducing the level of thermal distortion. Ultimately,the quality of the transcription of the reticle pattern onto the waferis improved.

Accordingly, in one aspect, the invention is directed to a reflectivereticle that includes:

substrate having an active region on a first surface of the substrate;and

at least one non-active region on a second surface of the substratewherein each non-active region is characterized by having a surface thatis formed of material that has an emissivity that is higher than that ofthe materials forming the active region surface.

In another aspect, the invention is directed to photolithography systemthat includes:

a source of extreme ultraviolet radiation;

means for collecting the radiation emitted from the source of extremeultraviolet radiation and forming a light beam therefrom that isdirected to an active region of a reflective reticle, wherein thereflective reticle includes:

(i) a substrate having an active region on a first surface of thesubstrate; and

(ii) at least one non-active region on a second surface of the substratewherein each non-active region is characterized by having a surface thatis formed of material that has an emissivity that is higher than that ofthe materials forming the active region surface; and

a wafer disposed downstream from the reflective reticle.

In a further embodiment, the invention is directed to a process forfabrication of a device comprising at least one element having adimension ≦0.25 μm, such process comprising construction of a pluralityof successive levels, construction of each level comprising lithographicdelineation, in accordance with which a subject active region of areflective reticle is illuminated to produce a corresponding patternimage on the device being fabricated, ultimately to result in removal ofor addition of material in the pattern image regions, in whichillumination used in fabrication of at least one level is extremeultra-violet radiation, characterized in that the process employs theinventive reflective reticle.

Modeling studies suggest that emissivity engineering can effectivelyreduce the distortions especially for reflective silicon reticles. Forsilicon reticles, simulations have shown an 82% reduction in totalplacement errors and a 25% reduction in residual placement errors.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of an EUV lithography device;

FIGS. 2A and 2B are plan and cross-sectional views, respectively, of areflective reticle;

FIG. 3 is a schematic of a dark field reticle; and

FIG. 4 is a schematic of a half dark/half bright field reticle.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 schematically depicts an apparatus for EUV lithography thatcomprises a radiation source 11, such as a synchrontron or a laserplasma source, that emits x-rays 12 into condenser 13 which in turnemits beam 14 that illuminates a portion of reticle or mask 15. Theemerging patterned beam is introduced into the imaging optics 16 whichprojects an image of reticle or mask 15, shown mounted on mask stage 17,onto wafer 18 which is mounted on stage 19. Element 20, an x-y scanner,scans reticle 15 and wafer 18 in such direction and at such relativespeed as to accommodate the desired mask-to-image reduction.

The wafer is preferably housed in a wafer chamber that is separated fromthe other elements of the photolithography system located upstream asillustrated in FIG. 1. These other elements can be housed in one or morechambers which are preferably maintained in vacuum to minimizeattenuation of the x-rays. EUV radiation projected from the reticle andtranslated by the camera travels through an aperture in the waferchamber.

The EUV lithography device of the present invention is particularlysuited for fabricating integrated devices that comprise at least oneelement having a dimension of ≦0.25 μm. The process comprisesconstruction of a plurality of successive levels by lithographicdelineation using a mask pattern that is illuminated to produce acorresponding pattern image on the device being fabricated, ultimatelyto result in removal of or addition of material in the pattern imageregions. Typically, where lithographic delineation is by projection, thecollected radiation is processed to accommodate imaging optics of aprojection camera and image quality that is substantially equal in thescan and cross-scan directions, and smoothly varying as the spacebetween adjacent lines varies. In a preferred embodiment, projectioncomprises ringfield scanning comprising illumination of a straight orarcuate region of a projection reticle. In another preferred embodiment,projection comprises reduction ringfield scanning in which an imagedarcuate region on the image plane is of reduced size relative to that ofthe subject arcuate region so that the imaged pattern is reduced in sizerelative to the reticle region.

The individual elements that form the EUV lithography device as shown inFIG. 1 can comprise conventional optical devices, e.g., condensers,cameras, and lens, for projection EUV lithography. Preferably the EUVLdevice employs a condenser that collects soft x-rays for illuminating aringfield camera. A particularly preferred EUVL device that employs acondenser having a diffraction grating on the surface of a mirrorupstream from the reflective mask that enhances critical dimensioncontrol is described in Sweatt et al., U.S. patent application Ser. No.09/130,224 entitled “Diffractive Element in Extreme-UV LithographyCondenser” filed on Aug. 6, 1998 which is incorporated by reference. Thecondenser illustrated therein has the ability to separate the light froma line or quasi point source at the entrance pupil into severalseparated lines or transform point foci that are still superimposed oneach other at the ringfield radius, thus maximizing the collectionefficiency of the condenser and smoothing out any inhomogeneties in thesource optics.

FIG. 2A shows a reflective reticle 30 having a generally circularperimeter; it is understood that the perimeter of reflective reticle forthe present invention can have any figure including, for example,polygons. The surface of the reflective reticle includes an activeregion 39 where the mask pattern is formed. During projection printing,EUV radiation is reflected from the active region and onto the wafer.The surface of the reflective reticle also includes non-active regions32, 34, 36, and 38. EUVL preferably employs an x-ray radiation source atabout 13 nm, but the absorption at this wavelength is very strong inessentially all materials; therefore, EUVL employs reflective opticssuch as Mo/Si multilayer mirrors. The multilayer mirror, which typicallyranges from about 280 nm to 320 nm in thickness, can also be made from,for example, Mo/Be. The strong x-ray absorption also necessitates theuse of reflective mask or reticle patterns which are typically made bydepositing absorber patterns on top of the Mo/Si multilayer mirror asdescribed, for instance, in U.S. Pat. No. 5,052,033, and D. M. Tennantet. al., Appl. Opt. 32, 7007 (1993), which are incorporated herein byreference.

FIG. 2B shows the cross-section of inventive reflective reticle thatcomprises a silicon substrate 40 having a mask pattern that comprises amultilayer mirror structure 42 onto which absorber patterns 48 and 50are deposited. Silicon substrates that are doped, e.g., by arsenic,boron, or phosphorus, are preferred since they have higher emissivitylevels than pure silicon. Absorber materials typically comprisestungsten, titanium, titanium nitride, or aluminum. As illustrated inFIG. 2B, non-active regions 44 and 46 do not include the multilayerreflective structure, rather, in this embodiment, the surface of thenon-active regions is bare or exposed silicon. As described herein, ithas been demonstrated that not covering the non-active regions with themultilayer reflective structure or any low emissivity material reducesthermal distortion. The reflective reticle as illustrated in FIG. 2B canbe made by conventional methods. During the fabrication process, thesurface of the silicon substrate corresponding to non-active regions 44and 46 is covered with photoresist so that subsequent sputtering of theMo/Si multilayer coating will not deposit any of the reflectivesubstances onto these regions.

In addition to constructing the nonactive regions with high emissivitysurface materials, further reduction of reticle thermal distortion canbe achieved by choosing materials with higher emissivity in fabricatingthe active regions. For example, in selecting the absorber material, TiNis preferred because of its high emissivity relative to most otherabsorber materials. Analogous selection of high emissivity materialsfrom among suitable candidates, with respect to other parts of theactive regions, can be employed.

Instead of forming non-active regions having bare silicon surfaces, thenon-active regions can comprise regions of the substrate that arecovered with a suitable high emissivity material. As is apparent, theuse of any substrate compatible material which has an emissivity that ishigher than that of the materials forming the active region shouldenhance heat dissipation. When the multilayer structure of the activeregion is made Mo/Si, which as an emissivity of about 0.12, then thesubstrate covering material must have an emissivity of greater than0.12. However, preferably this substrate covering material has anemissivity of greater than 0.25, and more preferably greater than 0.40.Suitable high emissivity materials include, for example, metal oxides,e.g., aluminum oxide, copper oxide and molybdenum oxide. From apractical standpoint, given that silicon has an emissivity of 0.72,thermal dissipation will not be significantly enhanced unless thesubstrate covering material has a very high emissivity value.

As is apparent, for any reflective reticle, the higher the ratio of thenon-active region surface area to the active region surface area, thegreater the reduction in thermal distortion will be when the non-activeregion is fabricated without the multilayer reflective structure or iscovered with a high emissivity substrate covering material. While thepresent invention is applicable even if this ratio is small, typicallythe combined surface area of the non-active regions will range fromabout 50% to about 60% and preferably at least about 25% and morepreferably at least about 40% of the total surface area of thereflective reticle.

A series of simulations were performed to examine the effect ofemissivity engineering to reduce the thermal distortions of reflectivesilicon reticles during scanning. Specifically, the simulation measuredthe placement errors and blurs associated with conventional andinventive reflective reticles. Placement error is defined as the errorin position of a point on the reticle just prior to the arrival of theillumination. Blur is defined as the motion of a point during the timethat it is illuminated.

FIGS. 3 and 4 show schematics of a 200 mm diameter by 0.75 mm thicksilicon wafer and the active reticle region used for the simulation. Thedimensions of the reticle were 130 mm in the direction of the scan and104 mm normal to the scan. The width of the illumination field was 6 mmand the height was 104 mm. The scan velocity was 38.7 mm/sec. The heatflux in the illumination field was 0.76 mW/mm². This flux corresponds tothe power required to expose 10 wafers/hour with a resist sensitivity of10 mJ/cm². The simulation was started with the leading edge of theillumination field aligned with the edge of the reticle. The effect offraming blades was taken into account in this analysis so that thesimulated illumination exposed only the active reticle region of thewafer and not the surrounding areas. Dark field and half dark/halfbright field reticles were simulated. A schematic of the half dark/halfbright reticle configuration is shown in FIG. 4. The dark field reticleconservatively assumes that all incident energy was absorbed. The halfdark/half bright field mask assumes all incident energy is absorbed onthe dark region and approximately 42 percent is absorbed in the brightregion. At the reticle, the integrated average reflectivity for Mo/Si isapproximately 58%. The emissivities of the bright and dark fields werebased on actual measurements. The emissivity of the Mo/Si coating was0.122, and that of a tungsten absorber material was 0.037. Outside theactive region of the reticle, the Mo/Si coating was not deposited. Thisregion was assumed to be bare silicon with an emissivity of 0.72. Thereticle was also allowed to expand freely. This assumption in effectneglected the frictional and electro-static forces on the reticle fromthe chuck.

The technique used in the finite element analysis to simulate the movingillumination source included the step of tagging all element faces inthe active reticle region, and at each time step determining which ofthe faces were within the bounding area of the moving source. Simplelinear equations of motion with constant velocity were used to describethe location of the leading and trailing edges of the source. Finiteelement faces which lied fully or partially within the boundary of themoving source had an appropriate heat flux boundary condition appliedcorresponding to the flux within the source and the fraction of the facethat lied within the location the source. The silicon materialproperties used for the simulations are given as follows:

Density (Kg/m³) 2330.0 Thermal Conductivity (W/m K) 148.0 Specific Heat(J/kg K) 712.0 Young's Modulus (GPa) 107.0 Poissons Ratio 0.25Coefficient of Thermal Expansion 2.5E-06

The following table provides distortion comparisons for siliconreflective reticles with full Mo/Si coating and bare silicon outside theactive region.

Half Half Bright Dark Field Bright Half Dark Dark Field Bare Si HalfDark Bare Si Condition/ Full Mo/Si Outside Full Mo/Si Outside DistortionCoating Active Coating Active Total 1457.8 259.87 879.3 184.6 Placement(nm) Residual 6.64 4.97 7.65 7.65 Placement (nm) Blur (nm) 0.67 0.690.72 0.70

These simulation results strongly suggest that for both dark and halfdark/half bright pattern densities, low distortion reticles can bedesigned using emissivity engineering approaches. In particular, it isdemonstrated that by coating only the active region of the reticle withMo/Si and absorber, and leaving the non-active region uncoated, asignificant reduction in total distortion can be achieved.

Although only preferred embodiments of the invention are specificallydisclosed and described above, it will be appreciated that manymodifications and variations of the present invention are possible inlight of the above teachings and within the purview of the appendedclaims without departing from the spirit and intended scope of theinvention.

What is claimed is:
 1. A reflective reticle for extreme ultravioletlithography comprising: a substrate having an active region on a firstsurface of the substrate wherein the active region comprises (1) aradiation reflective material that is coated on the first surface of thesubstrate and (2) a pattern comprising a radiation absorbing materialformed on the radiation reflective material wherein the pattern ofradiation absorbing material partially covers the radiation reflectivematerial wherein the active region defines an outer perimeter situatedwithin the substrate perimeter; and at least one non-active region on asecond surface of the substrate wherein the at least one non-activeregion is characterized by having a surface that is formed of materialthat has an emissivity that is higher than that of the radiationreflective material of the active region surface wherein the at leastone non-active region is positioned along the outer perimeter of theactive region and wherein the at least one non-active region has acollective surface area that is at least 25% of the collective surfacearea of the first and second surfaces of the substrate.
 2. Thereflective reticle of claim 1 wherein the at least one non-active regiondoes not comprise a layer of radiation reflective material.
 3. Thereflective reticle of claim 1 wherein the radiation reflective materialhas a multilayer structure formed of material that is selected from thegroup consisting of (a) molybdenum and silicon, and (b) molybdenum andberyllium.
 4. The reflective reticle of claim 3 wherein the radiationreflective material has a thickness of between 280 nm to 320 nm.
 5. Thereflective reticle of claim 3 wherein radiation absorbing material isselected from the group consisting of tungsten, titanium, titaniumnitride, aluminum and mixtures thereof.
 6. The reflective reticle ofclaim 1 wherein the at least one non-active region is characterized byhaving a surface that is formed of material that has an emissivity of atleast 0.25.
 7. The reflective reticle of claim 1 wherein the at leastone non-active region is characterized by having a surface that isformed of material that has an emissivity of at least 0.40.
 8. Thereflective reticle of claim 1 wherein the at least one non-active regionhas a collective surface area that is at least 40% of the collectivesurface area of the first and second surfaces of the substrate.
 9. Thereflective reticle of claim 1 wherein the active region defines arectangularly-shaped surface having four sides and the at least onenon-active region comprises four non-active regions each of whichborders a side of the rectangularly-shaped surface.
 10. The reflectivereticle of claim 1 wherein the substrate is made of silicon.
 11. Areflective reticle for extreme ultraviolet lithography comprising: asubstrate made of silicon having an active region on a first surface ofthe substrate wherein the active region comprises (1) a radiationreflective material that is coated on the first surface of the substrateand (2) a pattern comprising a radiation absorbing material formed onthe radiation reflective material wherein the pattern of radiationabsorbing material partially covers the radiation reflective materialwherein the active region defines an outer perimeter situated within thesubstrate perimeter; and at least one non-active region on a secondsurface of the substrate wherein the at least one non-active regioncomprises an exposed surface of the silicon substrate wherein the atleast one non-active region is positioned along the outer perimeter ofthe active region and wherein the at least one non-active region has acollective surface area that is at least 25% of the collective surfacearea of the first and second surfaces of the substrate.
 12. Thereflective reticle of claim 11 wherein the radiation reflective materialhas a multilayer structure formed of material that is selected from thegroup consisting of (a) molybdenum and silicon, and (b) molybdenum andberyllium.
 13. The reflective reticle of claim 12 wherein the radiationreflective material has a thickness of between 280 nm to 320 nm.
 14. Thereflective reticle of claim 12 wherein radiation absorbing material isselected from the group consisting of tungsten, titanium, titaniumnitride, aluminum and mixtures thereof.
 15. The reflective reticle ofclaim 11 wherein the at least one non-active region has a collectivesurface area that is at least 40% of the collective surface area of thefirst and second surfaces of the substrate.
 16. The reflective reticleof claim 11 wherein the active region defines a rectangularly-shapedsurface having four sides and the at least one non-active regioncomprises four non-active regions each of which borders a side of therectangularly-shaped surface.
 17. A reflective reticle for extremeultraviolet lithography comprising: a substrate having an active regionon a first surface of the substrate wherein the active region comprises(1) a radiation reflective material that is coated on the first surfaceof the substrate and (2) a pattern comprising a radiation absorbingmaterial formed on the radiation reflective material wherein the patternof radiation absorbing material partially covers the radiationreflective material wherein the active region defines an outer perimetersituated within the substrate perimeter; and at least one non-activeregion on a second surface of the substrate wherein the at least onenon-active region is characterized by having a surface that comprises ametal oxide that has a higher emissivity than that of the radiationreflective material of the active region surface wherein the at leastone non-active region is positioned along the outer perimeter of theactive region and wherein the at least one non-active region has acollective surface area that is at least 25% of the collective surfacearea of the first and second surfaces of the substrate.
 18. Thereflective reticle of claim 17 wherein the at least one non-activeregion does not comprise a layer of radiation reflective material. 19.The reflective reticle of claim 17 wherein the radiation reflectivematerial has a multilayer structure formed of material that is selectedfrom the group consisting of (a) molybdenum and silicon, and (b)molybdenum and beryllium.
 20. The reflective reticle of claim 19 whereinthe radiation reflective material has a thickness of between 280 mn to320 nm.
 21. The reflective reticle of claim 19 wherein radiationabsorbing material is selected from the group consisting of tungsten,titanium, titanium nitride, aluminum and mixtures thereof.
 22. Thereflective reticle of claim 17 wherein the at least one non-activeregion is characterized by having a surface that is formed of materialthat has an emissivity of at least 0.25.
 23. The reflective reticle ofclaim 18 wherein the at least one non-active region is characterized byhaving a surface that is formed of material that has an emissivity of atleast 0.40.
 24. The reflective reticle of claim 17 wherein the at leastone non-active region has a collective surface area that is at least 40%of the collective surface area of the first and second surfaces of thesubstrate.
 25. The reflective reticle of claim 17 wherein the activeregion defines a rectangularly-shaped surface having four sides and theat least one non-active region comprises four non-active regions each ofwhich borders a side of the rectangularly-shaped surface.